Must satire be based upon a real or perceived truth?
Satire is founded in truth. The beauty of good satire is that it's subject matter usually communicates what 'everyone' probably sees and feels, however for one reason or another 'everyone' perfers to deny its truth or reality.The use of satire whether in the circles of literature, politics, or history is a devise used by the author to provoke a truth that lies just under the surface of acceptability or respectability. Satire allows the author who lives within the traps of status-quo respectibility to escape its claws, and at the same time send a powerful message to the status-quo respectables. In many ways a good satirical writer possess a unique talent. He or she is able to force the mediocrity out of the individual, and in its stead whether they believe the authors point of view or not, realize it's okay to think for themself.
Mark Twain is a master of satire. If you read him, you will understand the power of satire.
Satire is based on human frailties and follies. The concept of truth is dependent on perspectives, but yes, I believe there must be some type of "truth" the author is trying to uncover by the use of sarcastic humor. Making fun of values and ideas that we don't agree with has been a literary form since the early Greek writings.
From THE COLUMBIA ENCYCLOPEDIA:
"From ancient times satirists have shared a common aim: to expose foolishness in all its guises — vanity, hypocrisy, pedantry, idolatry, bigotry, sentimentality — and to effect reform through such exposure. The many diverse forms their statements have taken reflect the origin of the word satire, which is derived from the Latin satura, meaning "dish of mixed fruits," hence a medley"